FUNCTIONS OF SENSORY GANGLION. 329 



any knowledge, in which there is not the rudiment of a Cerebrum, the En- 

 cephalon being only represented by a single ganglionic mass, which, from its 

 connection with the nerves of sense, must obviously be regarded as analogous 

 to the congeries of ganglia that we find in the higher forms of the class. 



a. It has been supposed, from the results of an imperfect examination of this very remarka- 

 ble animal, that it is altogether destitute of Encephalon ; and that it possesses no ganglionic 

 centre, except the Spinal Cord and Medulla Oblongata. The researches of M. de Quatre- 

 fages, however, indicate that the most anterior of the ganglionic enlargements exhibited by 

 its Cerebro-Spinal axis, is of a more special character than the rest; uniting in itself the 

 characters of several distinct ganglionic centres. The ganglionic enlargements, arranged in 

 a linear series, which altogether represent the Spinal Cord, each give origin to a single pair 

 of nerves; but the cephalic ganglion is the centre of five pairs. Of these, the first pair is 

 distinctly an Optic nerve; being exclusively distributed to an organ, which has the structure 

 of a rudimentary Eye, though lodged within the dura mater; reminding us, in its situation, 

 of the Auditory apparatus of the Gasteiopod Mollusks, which is actually imbedded in the 

 posterior part of the Cephalic ganglia. The second pair seems to correspond in its distribu- 

 tion with the Facial; whilst the third represents the Fifth pair and the Pneumogastric con- 

 jointly. The fourth find fifth pairs are distributed to the fin-like expansion, which forms the 

 margin of the head as well as of the body; and seem to hold the same relation to the two 

 preceding pairs, as the dorsal branches of the Spinal nerves bear to the ventral, or, in Man, 

 the posterior to the anterior. Hence we see that this single ganglion is made up of at least 

 three centres; of which the first corresponds to the Optic ganglion of higher Vertebrata; 

 whilst the second and third are analogous to certain parts of the Medulla Oblongata in im- 

 mediate connection with them. Moreover, this little animal possesses an organ of Smell, 

 much more distinct than the rudimentary eye; and although its connection with the anterior 

 part of the cephalic ganglion has not yet been traced (owing to the extreme minuteness of 

 the parts, and the difficulty resulting from the interposition of the dura mater, which is in 

 equally close contact with the nervous mass which it incloses, and with the olfactive organ 

 which abuts upon its exterior), there can be little doubt that such a connection exists, and 

 that the Cephalic mass unites within itself also the characters of an Olfactive ganglion. But 

 no part whatever can be traced, which bears any resemblance to the Cerebral hemispheres; 

 and as these, wherever they exist, are completely isolated from the Sensory ganglia, their 

 absence may be stated as an almost certain fact. Hence, in this particular, the Amphioxus 

 evidently corresponds with the Invertebrata; to which its affinity is so close in other particu- 

 lars, that many Naturalists have hesitated to assign it a place in the Vertebrated series at all; 

 and, as will be seen in the next paragraph, the union of several really distinct ganglionic 

 centres into one Cephalic mass, is a fact which is capable of actual demonstration. (See 

 the Memoir on the Branchiostoma or Amphioxus, by M. de Quatrefages, in the Annales des 

 Sciences Naturelles, 3 me Serie, Zoologie, torn, iv.) 



426. Descending to the Invertebrated series, we find that, except in a few 

 of those which border most closely upon Vertebrata (such, for example, as 

 the Cuttle-Fish), the whole Cephalic mass appears to be made up of ganglia, 

 in immediate connection with the nerves of sense. These may appear to 

 form but a single pair ; yet they are in reality composed of several pairs, 

 fused (as it were) into one mass. Of this we may judge by determining the 

 number of distinct pairs of nerves which issue from them ; and also by the 

 investigation of the history of their development, the results of which bear a 

 close correspondence with those obtained in the preceding method. 



a. Thus, Mr. Newport has shown, by studying the development of the head in certain 

 species of the class Myriapoda, that it is originally composed of no less than eight segments; 

 each having its peculiar appendages; and each possessing (like the segments of the body) 

 its own pair of ganglionic centres. These segments afterwards coalesce into two portions ; 

 of which the most anterior, made up by the union of four sub-segments, is termed the pro- 

 per cephalic; whilst the posterior, also made up of four sub-segments, is termed the basilar. 

 The four pairs of ganglia belonging to the cephalic portion coalesce into the one pair of 

 cephalic ganglia; whilst the other four pairs unite to form the first sub-assophageal ganglia. 

 The first of the original sub-segments had, as its proper appendages, the antennae; and the 

 ganglia contained in it were evidently the proper centres of the antennal nerves. The 

 second had no movable appendages, but contained the eyes; and its ganglia were evidently 

 the proper centres of the optic nerves. To the third belonged the first pair of jaws, the 

 maxillae; and to the fourth, the maxillary palpi: and these organs derived nerves from their 



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